The afore-mentioned elements, viz. so-called mounting elements, pushbutton switches and auxiliary tools, such as clamping means, are adequately known and in use with work processing so that no detailed description of such elements is necessary.
Modern production plants operate with so-called work pallets on which the workpieces to be processed are clamped by suitable clamping means. During processing of the workpiece(s) on one pallet, a second pallet is usually loaded with workpieces and held on stand-by. Once the workpieces of the first pallet are processed, the first pallet is moved out of the processing station and the second stand-pallet is moved in for being processed. Subsequently, the operators will remove the finished workpieces from the moved-out pallet and reload the pallet with workpieces to be processed, it being desirable to perform the clamping of the workpieces on the pallets through a pressure medium, preferably hydraulically, to attain a uniformly repeatable pressure for a uniform and precise processing. One problem resides in that it is not possible to provide each pallet with a hydraulic aggregate and that means will have to be provided to hold the hydraulically locked clamping elements in their clamping position after the hydraulic aggregate has been disconnected. During processing of the workpieces in the processing station, care must be taken to prevent the clamping pressure from dropping since otherwise damage would be done to the expensive facilities of the processing station. Hitherto, this problem was solved by so-called pressure accumulator units, with a hydraulic accumulator being disposed between the hydraulic aggregate and the hydraulic clamping elements which, after disconnection of the hydraulic aggregate, compensates for any pressure fluctuations caused e.g. by temperature differences. However, such accumulations frequently fail due to their low storage capacity or in the event of leakage in the system. Attempts have frequently been made in the past to insure early identification of any pressure losses, by means of pressure control switches to preclude damage, especially to the expensive tools of the processing machine. Although the operation of such switches is satisfactory, this solution, on the one hand, involves substantial efforts as corresponding systems operate on pressure accumulators on the workpiece pallets or, on the other hand, the pressure control switches must be directly wired to the control of the processing machine.
It is, therefore, an object of the invention to provide a compact device, especially one not requiring a pressure accumulator and, hence, needing little space, to which one or more auxilary tools, such as clamping means actuatable by fluid pressure may be connected and which is capable of acting, in the event of a predetermined pressure decrease, on the processing machine, without wiring the device to the machine.